UNIVERSITY    OF    CALIFORNIA     AGRICULTURAL   EXPERIMENT  STATION 
COLLEGE   OF  AGRICULTURE  BENJ'  '°E  WHEELER-  •■"«•«" 

THOMAS    FORSYTH    HUNT,    Dean  AND  DIRECTOR 
BERKELEY  H.    E.    VAN    NORMAN,   Vice-Director    ano    Dean 

University  Farm  School 

CIRCULAR  No.  205 
August,  1918 

BLACKLEG 

WITH    NEW   METHODS    FOR   ITS    PREVENTION 
AND   TREATMENT 

By  GEO.  H.  HAET 


Blackleg  is  one  of  the  common  and  probably  the  best  known  of  any 
of  the  infections  diseases  of  cattle.  Most  cattlemen  of  any  experience 
under  range  conditions  have  come  in  contact  with  the  disease.  It  is 
prevalent  throughout  the  western  range  country  of  the  United  States 
and  is  quite  generally  distributed  throughout  the  world.  Few,  if  any. 
live  stock  counties  in  California  are  entirely  free  from  it.  Some 
have  claimed  such  freedom  for  years,  only  to  find  on  careful  investi- 
gation that  animals,  supposed  to  be  dying  from  other  causes,  were  in 
reality  infected  with  this  disease.  It  is  the  common  cause  of  sudden 
deaths  in  bovine  animals  between  six  months  and  two  years  of  age, 
and  when  such  animals  are  dying  it  should  be  the  first  disease  to  be 
considered  in  ascertaining  the  cause.  While  it  is  more  prevalent  on 
the  ranges,  young  cattle  on  dairy  pastures  in  some  sections  of  this 
state  have  to  be  regularly  vaccinated  to  prevent  losses. 

CAUSE  AND    METHOD   OF   INFECTION 

The  cause  of  the  disease  is  a  rod-shaped  micro-organism  known  as 
the  Bacillus  of  Blackleg.  This  organism  is  strictly  anaerobic,  mean- 
ing that  it  will  not  multiply  in  the  presence  of  the  oxygen  of  the  air. 
When  it  meets  with  unfavorable  conditions,  it  forms  spores  which  are 
the  resting  stage  of  the  bacteria  and  are  very  resistant  to  adverse 
conditions.  It  is  the  spores  which  infect  the  soil,  where  they  will 
remain  alive  for  j^ears.  When  they  infect  a  susceptible  animal,  they 
must  gain  entrance  through  a  comparatively  slight  wound  of  a  pene- 
trating nature  which  does  not  tear  open  the  skin  or  mucous  membrane 
and  allow  oxygen  of  the  air  to  come  in  contact  with  the  underlying 
tissue.  Such  injuries  to  the  skin  may  be  made  by  briers,  sharp  sticks, 
barbed  wire,  etc.,  through  which  wounds  the  bacteria  enter.  The 
disease  is  practically  confined  to  cattle,  although  very  rarely  sheep, 
goats,  and  even  hogs  have  been  known  to  contract  it. 

Seasons  have  a  marked  influence  on  the  disease.  It  is  most  liable 
to  make  its  appearance  in  the  late  summer  and  fall,  following  which 
it  is  most  prevalent  in  the  spring,  but  it  has  been  found  in  California 
at  all  times  of  the  year. 


SYMPTOMS 

In  many  cases  the  first  evidence  of  the  disease  is  the  finding-  of  one 
or  more  dead  animals  with  a  local  swelling  nnder  the  skin.  The  time 
between  which  the  organism  gains  access  to  the  body  and  the  first 
symptoms  appear,  known  as  the  period  of  incubation,  is  from  one  to 
three  days.  The  symptoms  are  both  local  and  general.  There  is  a 
marked  rise  of  temperature,  with  loss  of  appetite  and  dullness,  and 
the  animal  fails  to  keep  up  with  the  herd.  This  is  accompanied  with 
or  soon  followed  by  a  characteristic  local  swelling  on  some  part  of 
the  body.  The  swelling  appears  suddenly  and  contains  gas  formed 
by  the  bacteria  which  gives  it  a  peculiar  crackling  feeling.  It  varies 
in  size  in  different  cases  often  beginning  as  a  small  area  and  spreading 
rapidly  in  extent  until  the  animal  dies.  It  never  occurs  below  the 
knees  or  hocks  but,  with  these  exceptions,  may  be  found  in  any  part 
of  the  body.  The  frequent  appearance  of  the  swelling  on  one  of  the 
legs  has  given  the  disease  its  name  of  blackleg  or  black  quarter.  The 
quarter  on  which  the  swelling  occurs  is  usually  stiff  and  the  animal 
goes  lame.  On  incising  the  area  the  animal  evinces  little  or  no  pain, 
and  a  dark-colored  fluid  is  exuded,  consisting  of  blood  and  broken- 
down  muscle  tissue  mixed  with  gas  bubbles  having  a  sweetish-sour 
odor  and  frothy  appearance.  The  area  should  be  incised  with  caution 
as  the  discharges  resulting  are  teeming  with  organisms  and  if  allowed 
to  drop  on  the  ground  will  add  further  infection  to  the  soil.  Atypical 
cases  of  blackleg  occur  with  no  local  swelling.  The  absence  of  swell- 
ing, therefore,  is  not  alone  sufficient  evidence  to  exclude  the  disease — 
but  in  the  vast  majority  of  cases,  careful  examination  will  reveal  a 
local  affected  area.  So,  also,  while  the  age  incidence  is  clearly  marked, 
cases  frequently  occur  up  to  three  years  of  age  and  at  times  even  in 
much  older  animals.  The  symptoms  develop  rapidly,  accompanied  by 
great  weakness  and  depression,  rapid  breathing,  and  occasionally  con- 
vulsions and  death  in  from  twenty-four  to  seventy-two  hours. 


POST-MORTEM    APPEARANCE 

The  important  things  to  observe  in  an  animal  dead  of  suspected 
blackleg  are  its  age,  the  local  swelling,  and  the  practically  normal 
spleen.  On  examining  the  carcass,  the  first  step  is  to  examine  for  the 
local  swelling  above  described.  On  removing  the  skin  over  the  area, 
a  large,  dark  swelling  involving  the  muscle  will  be  observed.  The 
muscle  affection  may  be  present  in  any  degree  from  slight  darkening 
of  the  normal  muscle  tissue  with  gas  bubbles  in  its  substance,  to  com- 
plete degeneration  of  the  muscle  in  the  center  of  the  area  to  a  semi- 
solid mass  filled  with  gas  bubbles.  The  peculiar,  somewhat  character- 
istic odor  of  the  disease  can  be  best  obtained  from  the  local  swelling. 
Internally,  there  is  a  general  congested  condition  of  the  organs  as  is 
seen  in  most  all  acute  infectious  diseases.  The  spleen,  however,  is 
not  enlarged.  The  liver  is  congested  and  may  show  a  mottled  colora- 
tion  on   its   surface.      There   may   be   present   ecchymoses   or   small 


hemorrhagic  spots  in  the  serous  membranes,  such  as  the  pericardium 
or  heart  sack,  pleura  or  lining  of  the  chest  wall  and  covering  of  the 
lungs  and  peritoneum,  or  covering  of  the  intestine  and  lining  the 
abdominal  walls.  The  lungs  are  congested  but  show  nothing  char- 
acteristic. 


Biological  preparations  used  in  prevention  and  treatment  of  blackleg. 


In  making  post-mortem  examinations  of  carcasses,  care  must  be 
taken  not  to  infect  the  soil  further.  Therefore,  the  work  is  to  be 
done  at  the  point  of  disposal  of  the  animal.  The  carcass  should  be 
burned  or  buried  deeply  after  covering  with  quicklime  and  the  con- 
taminated surface  soil  thrown  on  the  fire  or  into  the  burial  hole. 


DIFFERENTIAL    DIAGNOSIS 

There  are  other  diseases  with  which  blackleg  may  be  confounded, 
chief  of  which  is  anthrax.  The  latter  is  differentiated  from  blackleg 
by  the  fact  that  it  attacks  animals  of  all  ages  with  equal  frequency, 
as  well  as  all  species  of  domestic  animals  and  man.  In  some  cases  a 
local  swelling  is  present,  but  this  is  evidence  of  localization  and  is 
always  slower  in  development.  Animals  with  this  form  of  anthrax 
will  live  longer  than  blackleg  cases.  On  palpation  of  the  local  anthrax 
swelling,  no  crackling  sound  is  noticed  and,  on  cutting  into  same,  no 
gas  bubbles  are  present  and  the  blackleg  odor  is  absent.  On  post- 
mortem the  spleen  is  found  much  enlarged  and  softened  and  the  blood 
is  black  and  tarry,  clotting  imperfectly  or  not  at  all.  On  account 
of  the  danger  of  further  soil  infection  in  opening  anthrax  carcasses 
as  well  as  of  human  infection,  it  is  better  to  have  veterinary  or  labora- 
tory assistance  in  making  a  diagnosis.  (See  circular  from  this  station 
on  anthrax,  by  Haring). 

The  laboratory  diagnosis  of  blackleg  from  specimens  received  is 
unsatisfactory,  as  a  rule,  due  in  many  instances  to  the  character  of 
the  tissues  sent  and  to  more  or  less  decomposition  which  usually  occurs 
during  transit.  Under  these  conditions  the  isolation  of  the  causative 
organism,  which  is  difficult  at  best,  is  rendered  almost  impossible. 
Greater  dependence  should  therefore  be  placed  on  the  field  examin- 
ation, which  is  usually  sufficient  to  make  a  positive  diagnosis. 

Another  disease,  quite  common  in  California,  which  so  closely 
simulates  hemorrhagic  septicaemia  that  it  cannot  be  positively  differ- 
entiated from  it,  may  be  mistaken  for  blackleg.  This  disease,  however, 
affects  animals  of  all  ages.  Local  swellings  are  not  usually  present 
and  on  post-mortem  examination  extensive  hemorrhagic  blotches  and 
small  blood  spots  are  present  on  the  lining  and  covering  membranes 
of  the  body  cavities  and  organs. 


TREATMENT  AND  PREVENTION 

Powdered,  Pellet,  and  String  Vaccine. — Until  recently  no  remedy 
of  any  real  value  was  known  and  even  now  nearly  all  affected  animals 
die.  The  method  therefore  has  been  to  prevent  the  spread  of  the  dis- 
ease by  vaccinating  all  susceptible  animals  as  soon  as  the  disease  was 
found  or  in  a  great  many  cases  to  make  vaccination  the  procedure  on 
all  infected  lands  without  waiting  for  the  disease  to  make  its  appear- 
ance. This  vaccine  was  made  by  drying  the  affected  muscle  tissue 
from   animals   dead   of   blackleg.     It   was   then   ground   in   a   mill, 


moistened,  spread  out  on  thin  trays  and  subjected  to  heat  at  about 
95°  C.  for  six  hours,  which  weakens  or  attenuates  the  organisms. 
When  the  resulting  material  containing  the  powdered  muscle  tissue 
and  spores  is  injected  into  an  animal,  it  produces  a  mild  form  of  the 
disease  which  renders  the  animal  immune  from  natural  infection.  As 
originally  made  by  Arloing,  who  devised  the  method,  two  vaccines 
were  used,  the  first  being  subjected  to  a  higher  degree  of  attenuation 
than  the  second.  No.  1  vaccine  was  used  to  prepare  the  animal  to 
be  immunized  for  the  second  stronger  vaccine  given  ten  days  to  two 
weeks  later.  As  generally  used  at  present,  only  one  injection  is  given. 
After  heating  and  regrinding  the  vaccine  is  always  tested  on  guinea 
pigs  to  see  that  the  contained  organisms  have  been  properly  attenuated 
by  the  heat  before  sending  it  out. 

This  vaccine  in  powdered  form  has  been  put  out  by  the  U.  S. 
Bureau  of  Animal  Industry  free  of  charge  to  cattlemen  for  twenty 
years,  at  the  rate  of  from  one  to  several  million  doses  yearly.  Com- 
mercial biological  firms  have  been  making  the  same  vaccine  in  pellet 
as  well  as  string  form,  which  is  easier  to  administer,  and  are  selling- 
it  in  large  quantities  as  a  preventive  of  the  disease.  Many  stockmen 
have  used  this  vaccine  and  statistics  covering  millions  of  animals  so 
treated  as  a  whole  show  most  satisfactory  results. 

The  fact  remained,  however,  that  the  vaccine  could  not  be  properly 
standardized.  Its  activity  depended  on  the  presence  of  spores  of 
the  blackleg  organism.  To  give  proper  immunity  it  was  necessary 
for  these  spores  to  germinate  in  the  body  of  the  injected  animal.  There 
was  no  way  of  ascertaining  the  number  of  these  spores  and  one  vac- 
cine might  contain  few  while  another  would  contain  many.  In  spite 
of  the  guinea-pig  test  batches  of  vaccine  have  been  sent  out  which 
were  not  sufficiently  attenuated  by  the  heating  process,  and  resulted 
in  the  production  of  the  disease  in  the  less  resistant  of  the  injected 
animals  and  in  some  very  severe  losses.  At  other  times  sufficient 
spores  would  not  be  present  or  they  had  been  too  highly  attenuated 
by  heat,  so  that  no  immunity  was  produced  and  injected  animals 
woulel  continue  to  die  from  natural  infection.  Also  the  vaccine  had 
no  curative  effect  and  some  time  was  required  after  injection  before 
immunity  was  established,  during  which  time  losses  from  natural 
infection  would  continue.  It  was  these  facts  so  well  known  to  all 
workers  with  blackleg  vaccine,  both  in  the  laboratory  and  in  the 
field,  that  leel  to  the  development  of  what  may  be  called  the  new 
methods  of  treating  and  preventing  this  disease. 

Blackleg  Serum. — In  the  treatment  of  this  disease  there  is  now 
being  produced  a  blackleg  serum,  originated  in  Europe  by  Kitt, 
Vallee,  Leclainche  and  others.  This  is  prepared  in  the  usual  way 
of  making  serum  for  other  infectious  diseases.  Horses  or  cattle  are 
gradually  infected  with  blackleg  organisms  of  increasing  virulence 
and  numbers  until  they  can  withstand  enormous  doses  of  the  most 
virulent  strain  of  the  organisms  injected  directly  into  the  circulating 
blood.  These  animals  are  then  bled  from  the  jugular  vein  under 
asceptic  precautions  and  the  serum  allowed  to  separate   from  the 


G 

clotted  blood.  This  serum  contains  immune  bodies  against  the  black- 
leg organism  and  when  injected  into  an  affected  animal  in  sufficient 
doses  has  distinct  curative  properties.  In  smaller  doses  it  will  also 
protect  healthy  animals  against  the  disease  immediately.  The  effect 
produced  by  the  injection  of  such  a  serum  is  termed  passive  immunity, 
as  distinct  from  active  immunity,  which  is  produced  by  an  attack  of 
the  disease  or  by  causing  the  animal  to  pass  through  a  mild  form 
of  the  disease  such  as  is  caused  by  vaccination.  Passive  immunity  in 
this  disease  is  of  short  duration  and  cannot  be  depended  on  for  a 
longer  period  than  ten  days.  Unless  a  supply  of  serum  is  close  at 
hand,  blackleg-affected  animals  will  be  dead  before  they  can  be  treated. 

The  great  field  of  usefulness  of  the  serum  is -in  its  application  to 
all  susceptible  animals  in  a  valuable  herd  where  animals  have  already 
died,  to  produce  an  immediate  immunity  and  cessation  of  further 
cases  developing.  For  this  purpose  25  to  30  cubic  centimeters  are 
given  each  animal  with  a  hypodermic  syringe  under  the  skin.  As  a 
curative  in  animals  already  affected  several  injections  may  be  neces- 
sary with  much  larger  doses  of  from  100  to  200  cubic  centimeters.  In 
herds  where  serum  is  being  administered  it  is  well  to  take  tempera- 
tures of  the  animals  and  any  with  a  high  temperature  (104°  S\  or 
above)  should  be  considered  as  infected  with  the  disease  even  if  show- 
ing no  other  physical  signs.  Such  animals  should  be  given  100  cubic 
centimeters  or  more  of  serum  as  a  curative.  After  this  has  been  done 
and  the  disease  stopped,  it  must  be  followed  in  a  week  by  a  vaccination 
of  the  animals  to  produce  an  active  immunity,  which  is  much  more 
lasting.  The  cost  of  such  a  procedure  at  the  present  time  probably 
justifies  its  use  only  in  suddenly  appearing  severe  outbreaks  and  in 
valuable  pure-bred  animals.  Commercial  houses  are  charging  from 
3  to  4  cents  per  cubic  centimeter  for  the  serum,  depending  on  the 
quantity  purchased.  The  difficulty  with  the  serum  is  that  at  the 
present  time  no  definite  means  of  standardizing  it  have  been  perfected 
and  no  degree  of  potency  is  required.  If  further  field  trials  prove 
its  value  this  will  no  doubt  be  given  consideration. 

Tissue  Filtrate  and  Culture  Filtrate. — In  the  prevention  of  the 
disease  two  new  products  are  now  being  prepared.  These  are  both 
free  from  the  causative  organism  in  either  vegetative  or  spore  form 
and  therefore  cannot  produce  the  disease.  One  of  these  is  made 
directly  from  the  muscle  juices  of  affected  animals,  which  are  extracted 
by  pressure,  and  is  known  as  tissue  filtrate,  and  the  other  is  made 
by  growing  the  blackleg  organism  under  anaerobic  condition  in  the 
laboratory  in  a  special  medium  containing  meat,  and  the  product  is 
known  as  culture  filtrate.  The  term  filtrate  is  applied  because  the 
finished  products  are  filtered  through  specially  constructed  clay  filters 
of  such  fine  porosity  that  no  bacteria  are  allowed  to  pass.  The  tissue 
filtrate  or  extract  is  also  called  aggressin  in  the  literature  put  out 
by  the  commercial  laboratories  which  have  the  products  for  sale. 

The  tissue  filtrate  or  aggressin  was  developed  by  veterinarians  at 
the  Kansas  Agricultural  College,  and  the  culture  filtrate,  by  Nitta, 
of  the  University  of  Tokio,  in  Japan.    The  first  product  requires  the 


actual  production  of  the  disease  in  animals  to  obtain  the  affected 
muscle  tissue  and  juices.  A  great  amount  of  the  material  cannot  be 
obtained  from  one  animal.  It  can  be  readily  seen,  therefore,  that  its 
production  on  a  large  scale  would  involve  the  sacrifice  of  a  good  many 
young  cattle  and  its  cost  thereby  be  greatly  enhanced  over  that  of  the 
culture  nitrate.  Even  though  experiments  may  prove  the  protective 
value  of  the  tissue  filtrate  to  be  greater  than  that  of  the  culture 
filtrate,  this  difference  may  not  be  sufficiently  great  to  warrant  the 
increased  cost  of  the  former.  Further  experimentation,  backed  up 
by  field  trials,  is  required  on  this  point.  In  the  final  stages  of  manu- 
facture the  culture  filtrate  is  partially  evaporated  to  reduce  its  volume 
and  preserved  by  the  addition  of  glycerin.  The  present  cost  of  the 
culture  filtrate  is  from  15c  to  20c  per  dose,  depending  on  the  quantity 
purchased.  The  material  is  put  up  to  inject  in  1  cubic  centimeter  or 
5  cubic  centimeter  doses,  depending  on  the  degree  of  concentration. 
The  tissue  filtrate  costs  30  to  35  cents  per  dose  of  5  cubic  centimeters. 
Both  kinds  of  vaccine  are  in  liquid  form.  The  freedom  of  these 
products  from  the  blackleg  organism  is  greatly  in  their  favor  as  this 
precludes  the  setting  up  of  a  virulent  form  of  the  disease  through 
their  use.  A  considerable  number  of  laboratory  experiments  have 
clearly  demonstrated  that  these  products  have  distinct  immunizing 
value  and  these  have  been  backed  up  by  many  field  trials  on  a  con- 
siderable number  of  animals.  In  Japan  the  culture  filtrate  is  the 
only  means  of  immunization  at  present  in  general  use.  The  product 
is  tested  in  the  laboratory  on  guinea  pigs  before  it  is  ready  for  distri- 
bution. Further  standardization  would,  however,  be  desirable,  which 
would  include  toxicity  tests. 

Rather  extravagant  claims  have  been  made  for  these  products  with 
the  desire  to  get  them  into  general  use  against  the  competition  of  the 
older  and  cheaper  powdered  muscle  vaccine.  Chief  of  these  may  be 
mentioned  the  claim  that  they  will  produce  permanent  immunity  or 
at  least  immunity  until  the  animal  has  passed  the  susceptible  age  with 
one  injection.  At  the  present  time  there  does  not  seem  to  be  sufficient 
evidence  to  justify  such  claims.  Where  these  results  have  appeared 
to  be  obtained  under  field  trials  unusually  favorable  conditions  may 
have  prevailed.  The  degree  of  infection  of  ranges  undoubtedly  differs 
in  this  disease  as  it  does  in  anthrax.  Where  animals  have  passed 
through  the  susceptible  age  period  with  one  treatment  they  may  have 
been  on  very  slightly  infected  ranges.  Also,  animals  treated  as  year- 
lings or  older  might  pass  through  safely  with  one  treatment,  whereas 
animals  treated  at  six  months  of  age  under  the  same  conditions  might 
break  with  the  disease  as  short  two-year-olds.  Further  evidence  is 
necessary  before  any  conclusive  statements  can  be  made  on  this  sub- 
ject. This  station  is  very  anxious  to  obtain  such  evidence  and  to 
make  it  available  for  stockmen.  Any  data  along  this  line  which  are 
obtained,  therefore,  from  the  use  of  either  blackleg  serum  or  culture 
or  tissue  filtrate  would  be  gratefully  received  and  tabulated  by  this 
experiment  station  if  sent  to  the  Division  of  Veterinary  Science, 
University  of  California,  Berkeley. 


WHEN  TO  VACCINATE 

On  known  infected  ranges  cattle  owners  should  not  wait  for  the 
disease  to  appear  before  vaccinating  susceptible  animals.  As  there 
are  two  principal  seasons  for  the  disease  there  should  be  two  vacci- 
nation periods,  one  in  the  spring  and  the  other  in  the  fall.  The  vac- 
cination should  be  done  fifteen  to  thirty  days  before  the  time  when 
cases  have  usually  appeared  in  the  past.  As  a  general  practice,  the 
period  between  February  15  and  March  1  is  a  good  time  for  the  spring 
vaccination  and  from  August  15  to  September  1  for  the  fall  vaccina- 
tion. This  may,  of  course,  have  to  be  varied  depending  on  local 
conditions.  Young  animals  being  turned  out  on  unknown  ranges 
or  pastures  should  be  vaccinated  as  a  precautionary  measure.  It  is 
not  necessary  to  vaccinate  young  animals  on  dairies  or  in  small  valley 
communities  where  no  cases  of  the  disease  have  been  reported.  One 
should  not  brand,  castrate,  or  ear-mark  and  vaccinate  at  the  same 
time.  With  our  present  knowledge  it  is  safer  to  vaccinate  all  animals 
of  susceptible  age  at  each  vaccination  period.  It  may  save  the  life  of 
an  animal  at  times,  when  the  muscle  vaccine  is  used,  to  give  them 
the  double  vaccination.  In  this  case  No.  1  vaccine  should  be  given  ten 
days  to  two  weeks  before  No.  2  vaccine. 


SUMMARY 

Blackleg  is  quite  generally  prevalent  in  California.  Stock  owners 
should  suspect  the  disease  in  all  cases  where  animals  from  six  months 
to  two  years  of  age  die  suddenly  with  a  local  swelling. 

The  old  single  or  double  muscle  vaccine  for  blackleg  in  either 
powdered,  pellet,  or  string  form,  has  given  such  satisfactory  results 
for  so  many  years  that  its  continued  use  is  justified. 

Blackleg  serum  has  immediate  immunizing  and  curative  properties. 
Its  use  is  to  be  recommended  in  affected  animals  and  in  the  hope  of 
immediately  stopping  losses  in  already  infected  herds  where  animals 
are  dying  of  the  disease.  Its  immunizing  effects  in  healthy  animals 
are  not  permanent  and  it  must  be  followed  by  vaccine  or  filtrate  within 
a  week  to  ten  days. 

Both  culture  filtrate  and  tissue  filtrate  have  well-marked  im- 
munizing effects  on  cattle  against  blackleg.  Their  freedom  from  the 
causative  organism  is  greatly  in  their  favor. 

The  routine  use  of  either  of  these  preparations  by  cattlemen  is 
justified  under  our  present  knowledge.  In  time,  they  may  largely 
replace  the  old  method  of  vaccination. 

Culture  filtrate  of  sufficient  potency  is  of  equal  value  and  has 
advantages  in  manufacture  and  cost  over  tissue  filtrate. 

There  are  not  sufficient  data  available  to  substantiate  the  general 
statement  that  one  treatment  with  either  of  the  filtrate  vaccines  will 
confer  life  immunity. 


